Vertical shaft impact crushers (VSI-crushers) are used in many applications for crushing hard material like rocks, ore etc. U.S. Pat. No. 3,154,259 describes a VSI-crusher comprising a housing and a horizontal rotor located inside the housing. Material that is to be crushed is fed into the rotor via an opening in the top thereof. With the aid of centrifugal force the rotating rotor ejects the material against the wall of the housing. On impact with the wall the material is crushed to a desired size. The housing wall could be provided with anvils or have a bed of retained material against which the accelerated material is crushed.
The rotor of a VSI-crusher usually has a horizontal upper disc and a horizontal lower disc. The upper and lower discs are connected with a vertical rotor wall. The upper disc has an aperture for feeding material into the rotor. The material lands on the lower disc and is then thrown out of the rotor via openings in the rotor wall.
The material to be crushed is often abrasive. To extend the technical life of the upper and lower discs they are often lined with replaceable wear plates. The wear plates are made from an abrasion resistant material and are replaced when they are worn down.
U.S. Pat. No. 4,796,822 to Terrenzio describe wear plates made in pairs. At each rotor opening two wear plates are put on each of the upper and lower discs. One of the wear plates has a recess with the intention of collecting a bed of material for improved wear resistance. The wear plates interact with each other and are also held in place by a landing ring.
U.S. Pat. No. 4,896,838 to Vendelin describes wear plates made in pairs. A first wear plate locates against a gusset block provided at the inside of the rotor wall. A second wear plate holds the first wear plate in place by means of a bevel overlapping a corresponding bevel of the first wear plate.
The wear plates described above are difficult to replace and do not ensure a stable bed being built up against the vertical rotor wall.